Tunable whip antenna



il nnhP J. W. SHIREY TUNABLE WHIP ANTENNA Filed 001.. 9. 1967 INVENTOR JAMES W. SHIREY ATTORNEYS Nov. 17, 1970 United States Patent 3,541,554 TUNABLE WHIP ANTENNA James W. Shirey, Lakeland, Mich., assignor to L-Coil Research, Brighton, Mich., a partnership of Michigan Filed Oct. 9, 1967, Ser. No. 673,851 Int. Cl. H01q 1/32, 9/00 U.S. Cl. 343-713 6 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION The invention belongs to the art of whip antennas for mounting on a metallic body, such as a motor vehicle body, for use in mobile radio communications. Mobile radio communication equipment is designed to operate at a predetermined frequency within a substantially narrow frequency band, such frequency being generally of the order of several megacycles per second or megahertz (for example 27 rnHz., 150 rnHz., etc). The transmitters are often of low power (as for example in the 27 rnHz. band, citizen band, where such power is limited to less than 5 watts under FCC regulations), and it is therefore desirable to utilize an antenna having substantially great sensitivity.

Mobile whip antennas are generally mounted on a support base attached to the vehicle body, in an appropriate position such as on top of the roof, on top of the trunk, on top of the fender, etc. The support base mechanically supports a vertically extending radiating element forming the antenna, and there is often a coil spring connector interposed between the base and the radiating element so as to provide a flexible mechanical connection therebetween preventing damages from occurring when the radiating element collides with obstructions. The electrical connection between the antenna and the transceiver (transmitter-receiver) mounted on the vehicle is generally effected by way of a shielded coaxial cable wherein the inner conductor is connected to the antenna radiating element and the outer shield is grounded to the vehicle body or frame. The portion of the support base attached to the vehicle body is electrically connected to the cable shield and the cable inner conductor is insulated from the mounting base and is electrically connected to the radiating element either directly or through an induction coil designed to provide a matched impedance between the antenna and the transceiver output and which permits to reduce considerably the length of the radiating element.

SUMMARY OF THE INVENTION The present invention provides a tunable whip antenna having a pair of inductance coils placed in series between the end of the insulated inner conductor of the lead-in cable and a radiating element. The two coils are disposed in alignment with each other and an adjustable means, consisting preferably of a ring peripherally disposed with respect to the coils and longitudinally displaceable thereabout at the junction thereof, is provided for adjustably varying the mutual inductance between the coils so as to properly tune the antenna to an appropriate predetermined frequency and so as to properly match the antenna input to the transceiver output.

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The many objects and advantages of the invention will become apparent to those skilled in the art when the following description of an example of an embodiment of the invention is read in conjunction with the accompanying drawings wherein:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial perspective view of a motor vehicle provided with the whip antenna according to the present invention mounted on the top of the trunk lid of such vehicle;

F FIG. 2 is an elevational view of the whip antenna of FIG. 3 is a partial longitudinal sectional view about line 33 of FIG. 2; and

FIG. 4 is a partial longitudinal sectional view substantially about lines 44 of FIG. 2.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT Referring now to FIG. 1, there is shown a portion of the metallic body 10 of a conventional motor vehicle on which a whip antenna 12, according to the present invention, is aflixed in an appropriate position, preferably in a substantially vertical attitude. As shown in the drawing, whip antenna 12 is mounted on the top surface of the vehicle trunk lid 14, although it is obvious that the antenna can be mounted in any other appropriate position, such as, for example, the top of the vehicle roof, or either the front or rear fenders.

As shown in FIG. 1, and in more details of FIG. 2, whip antenna 12 comprises a conventional mounting base 16 having a fiat lower end face 17 and a hollow threaded stud 18 projecting through an appropriate aperture 20 in the metallic panel 22 of the vehicle body 10 and held in position by means of nut 24 and washer 26. Threaded stud 18 may also be used as an appropriate ground connection for the grounded conductor of lead-in cable 28 connecting the antenna to the radio transceiver, not shown, or the grounded conductor may be internally connected to base 16 in any appropriate conventional manner such that the grounded connector is electrically connected to the metallic panel 22 of the body 10 of the vehicle, such that the body forms a finite ground plane. The insulated conductor which, if a coaxial cable is used for cable 28, is the inner conductor, is adapted to pass through support base 16, without making electrical contact therewith, and is electrically connected to a fitting 30 electrically insulated from the finite ground plane. Fitting 30 mechani cally supports a coil spring 32 which in turn mechanically supports a hollow extension tubing or rod 34.

In order to insure perfect electrical connection between fitting 30 and hollow extension rod 34, a bypass wire 36 is disposed within the coil spring 32 between coil spring connector 38 and coil spring connecter 40 effecting the mechanical and electrical connection between the upper end of coil spring 32 and extension rod 34. Extension rod 34 is internally threaded at its upper end for mechanical and electrical connection to the internally threaded lower end of a short hollow rod member 42 by means of an externally threaded stud 44, as shown in FIG. 3. Short hollow rod member 42 in turn supports on its upper end a non-magnetic mandrel or rod such as a wood dowel 46, or the like, on the periphery of which are wound a pair of inductance coils 48 and 50 disposed electrically in series. Coil 48 is formed of a length of wire 52 wound with a predetermined number of turns, with the turns separated from each other by a predetermined distance. The lower end 54 of coil 48 is electrically connected to short hollow rod member 42 by way of a metallic fitting 56 attached to the lower end of wood dowel 46 and provided with an oblique cross aperture 58 in which passes the end portion 57 of wire 52. The lower portion of fitting 56 engages the inner bore of hollow rod member 42 and is provided with a plurality of slots, as shown at 60, disposed all the way through to a longitudinally disposed threaded bore 62 in which is engaged a screw 64 having a tapered head base 66, such that when screw 64 is drawn in, the diverse segments at the lower end of fitting 56 formed by slots 60 are spread apart such as to provide a strong mechanical connection between wood dowel 46 and short hollow rod member 42. At the same time, the end 57 of wire 52 is clamped between the peripheral surface of fitting 56 and the inner surface of the bore within hollow rod member 42.

As best shown in FIG. 4, the upper end of coil 50, which, in the example illustrated, is made of a predetermined number of contiguous turns of the same wire 52 as coil 48, is mechanically and electrically connected to a metallic sleeve 68 by way of fitting 70 and screw 72 structurally and functionally similar to fitting 56 and screw 64 previously described in detail. Sleeve 68 is internally threaded at its upper end, as shown at 74, for accepting a plug 76 having a threaded end 78 for engagement with inner thread 74. Plug 76 has on its upper end a small longitudinal blind bore 80 adapted to receive the lower end of a radiating rod element 82, having the conventional ball 84 on the top end thereof, as shown in FIGS. 1 and 2.

Coils 48 and 50 are covered with an insulating sleeve, shown best at 86 at FIGS. 2 and 4, and the peripheral surface of the sleeve corresponding to the junction between coil 48 and 50 is provided with a thread 88 permitting a thin ring or sleeve 90 having an appropriate internally threaded bore 92 to be longitudinally adjustably displaceable by rotation. Sleeve 90 is made of metal, preferably aluminum, and the longitudinal displacement thereof as the result of such rotation, varies the mutual inductance between coil 48 and coil 50, such that the antenna of the invention is adjustably tunable.

As an example of practical application, a whip antenna according to the present invention and adapted to operate in the citizen band frequency range (27 mHz.) has a radiating rod element 82, 17.75 inches in length, with an assembly for the coils consisting of short hollow rod member 42, wood dowel 46 and sleeve 68 and fitting 76 having a total length of 9.25 inches. Coil 50 is a single layer winding made of forty-four contiguous turns of No. 21 copper enameled wire, and coil 48 is made of thirtysix turns of the same wire with the turns spaced one eighth of an inch apart. Hollow rod or riser 34 is generally about five inches in length, although such length is not critical in view of the tunable property of the antenna.

After the antenna is installed on the motor vehicle and properly connected to the transciever by means of lead-in cable 28, the transceiver is operated in the transmitter mode and a field strength meter is placed proximate to the antenna while transmitting. A field strength reading is taken, and the longitudinal position of ring 90 is then adjusted by rotating the ring manually so as to displace it longitudinally up or down. The ring is longitudinally adjusted until the highest reading is obtained by way of the field strength meter. The ring 90 may then be immobilized in its appropriate position by means, for example, of one or more turns of adhesive tape.

Having thus described the invention by way of a practical embodiment thereof, modification whereof will be apparent to those skilled in the art, what is sought to be protected by Unted States Letters Patent is as follows:

1. A tunable antenna for use on a metallic motor vehicle and the like for electrical connection to a radio transceiver mounted on said vehicle by means of a twoconductor cable having a grounded conductor, said antenna comprising:

a conductive base adapted for mounting on said vehicle, said vehicle defining a finite ground plane; means for electrically connecting said grounded conductor to said base;

an elongated radiating top element;

a pair of separate inductance coils electrically and inductively in series;

the first of said inductance coils being a single layer winding of a predetermined number of turns having a first end electrically connected to said radiating element and a second end;

the second of said inductance coils being a single layer winding of a predetermined number of turns having a first end electrically connected to the second end of said first winding and a second end;

means for electrically connecting the other of said conductors of said two-conductor cable to the second end of said second winding; and

adjustable means for tuning said antenna by varying the mutual inductance coupling between said first and second windings.

2. The antenna of claim 1 wherein the windings of said first and second coils are separate consecutive windings on a common cylindrical non-magnetic mandrel.

3. The antenna of claim 2 wherein said adjustable means for varying the mutual inductanc between said first and second windings is a metal ring sleeve having an internal thread engaging an external thread formed on an insulating sleeve covering said first and second windings at the ends thereof connected together.

4. The antenna of claim 2 wherein said means for connecting said other of said conductors to the second end of said second winding comprises an electrically conductive metallic rod in series therebetween.

40 5. The antenna of claim 4 further comprising a flexible coil spring at least mechanically coupling said metallic rod to said base and a flexible conductor disposed within said coil spring for electrically connecting said metallic rod and said other of said conductors.

45 6. The antenna of claim 2 wherein said adjustable means for varying the mutual inductance between said first and second windings is a metal sleeve electrically insulated from said windings and disposed around the periphery of said windings at the ends thereof connected together, said metal sleeve being adapted to be displaced axially over the periphery of said windings at the ends thereof connected together.

References Cited UNITED STATES PATENTS 2,771,604 11/1956 Goldstein 343-888 x 2,875,443 2/1959 Kandoian 343 s95 2,894,260 7/1959 Ellis 343-745 66 2,941,204 6/1960 Bailey 343 713 3,085,215 4/1963 Shepherd 343-745 X 3,226,725 12/1965 Ritchie etal. -343 745 3,264,647 8/1966 Nuttle 343861 x 3,267,476 8/1966 Finke 343-715 HERMAN K. SAALBACH, Primary Examiner T. I. V-EZEAU, Assistant Examiner US. Cl. X.R.

Fibiafsh 22 3 33 UNITED STATES PATENT OFFICE CERTIFICATE OF. CORRECTION Patent No. 3,541,554 Dated November 17, 1970 Inventor(s) James W. Shirey' It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In THE SPECIFICATION ColxImn 1, line 29, delete "mHz'! in both instances and insert MHz line 30,. delete "mHz" and insert MHZ Column 3, line 43, delete "ml-I2" and insert MHz line 70, delete "Unted" and insert United mum MED .5 E. saflumm, M m Comissioner or Patem 

